Method for control of ionization electrostatic plating

ABSTRACT

In a plating process wherein a DC electrical potential is applied in a rare gas atmosphere between a positive electrode (anode) which is a boat containing a coating material and a negative electrode (cathode) which is an article subjected to plating so that glow discharge is induced and then the coating material in the boat is vaporized and the vaporized coating material is deposited fast on the article being plated, the present invention provides an improvement which comprises disposing a focusing tube and a dispersing torpedo, both of which are subjected to positive electrical potential, between the two electrodes. The electric lines of force formed between the two electrodes are focused by the focusing tube and dispersed by the torpedo. The pattern in which the electric lines of force are dispersed can easily be controlled by the position and shapes of the focusing tube and the torpedo and the magnitude of electric potential involved. By disposing the focusing tube and the torpedo so as to cause the electric lines of force to concentrate at specific parts of the article being plated, therefore, the vaporized and ionized coating material can be deposited fast on the article along the bundle of electric lines of force. Consequently, possible straying of the vaporized coating material can be minimized and, at the same time, the distribution of the film thickness of coating material to be deposited on the article can be freely adjusted.

United States Patent 1191 Matsubara [75] inventor: KiyoshiMatsubara,

Higashi-Murayama, Japan [73] Assignee: Agency of Industrial Science &

Technology, Tokyo, Japan [22] Filed: Feb. 12, 1973 [21] App]. No.: 331,494

204/169, 298; ll7/93.l GD, 93.3, 107, 93.44; 118/48, 49.1

[56] References Cited UNITED STATES PATENTS 3,054,697 9/1962 lrland et a1, 117/9344 3,055,775 9/1962 Crittenden et 211.. 118/491 3,192,892 7/1965 Hanson et a1 117/933 3,309,221 3/1967 Smith 117/931 GD 3,371,649 3/1968 Gowen 1124/49.] 3,434,876 3/1969 Stoudenheimer et a1. 117/93.1 GD 3,576,670 4/1971 Hammond 1 17/107 Primary Examiner-William D. Martin Assistant Examiner-John H. Newsome Attorney, Agent, or FirmKurt Kelman [57] ABSTRACT In a plating process wherein a DC electrical potential is applied in a rare gas atmosphere between a positive electrode (anode) which is a boat containing a coating material and a negative electrode (cathode) which is an article subjected to plating so that glow discharge is induced and then the coating material in the boat is vaporized and the vaporized coating material is deposited fast on the article being plated, the present invention provides an improvement which comprises disposing a focusing tube and a dispersing torpedo, both of which are subjected to positive electrical potential, between the two electrodes. The electric lines of force formed between the two electrodes are focused by the focusing tube and dispersed by the torpedo. The pattern in which the electric lines of force are dispersed can easily be controlled by the position and shapes of the focusing tube and the torpedo and the magnitude of electric potential involved. By disposing the focusing tube and the torpedo so as to cause the electric lines of force to concentrate at specific parts of the article being plated, therefore, the vaporized and ionized coating material can be deposited fast on the article along the bundle of electric lines of force. Consequently, possible straying of the vaporized coating material can be minimized and, at the same time, the distribution of the film thickness of coating material to be deposited on the article can be freely adjusted.

mm/ w fii 'METI'IOD FOR CONTROL OF IONIZATION ELECTROSTATIC PLATING BACKGROUND OF THE INVENTION This invention relates to a method for control of the plating operation in the ionization electrostatic plating method. It has heretofore been known that the socalled plating is accomplished in the atmosphere of a rare gas, such as argon gas, having a degree of vacuum on the order of to 10 torr by applying a DC electric potential between an anode which is the vaporizing source of coating material and a cathode which is an article subjected to plating, so that glow discharge occurs and the coating material is then vaporized at the vaporizing source. Consequently, the vaporized coating material is ionized and the ionized particles flow along courses conforming to the electric lines of power formed in the electric field between the two electrodes to be deposited on the surface of the article which serves as the cathode.

This process has already been known as an ion plating method. Since this method causes the ionized vapor of coating material to be deposited on the article which is simultaneously the cathode, it is advantageous over the universally known vacuum evaporation method in that possible straying of the coating material can be lessened and the coating material can be firmly deposited even on the reverse side of the article being plated. In plating performed by the said ion plating method, however, the amount of coating material which is scattered and lost is still large and the film of coating material which is deposited on the article cannot always be uniformized or made to acquire a desired thickness distribution.

An object of the present invention is to provide an ion plating method which minimizes possible straying of coating material in the course of plating and, consequently, enhances the efficiency of plating to a great extent.

Another object of this invention is to provide a method for the control of the ionization electrostatic plating operation, which method permits ready adjustment of the thickness distribution of the film of coating material to be formed on the article.

Still another object of this invention is to provide an ion plating method for easily forming a film of a desired alloy on the article.

SUMMARY OF THE INVENTION In the plating operation performed in the atmosphere of a rare gas by applying a DC electric potential between an anode which is a boat containing a coating material and a cathode which is an article subjected to plating so that glow discharge occurs and the coating material in the boat is then vaporized and the vaporized coating material is deposited on the article, the present invention accomplishes the aforementioned objects by disposing a focusing tube on the circumference of the bundle of electric lines of force formed in the electric field between the two electrodes and also disposing a dispersing torpedo at the center at which the electric lines of force are focused. Under application of positive potential, the focusing tube functions as an electrostatic lens to concentrate the electric lines of force emanating from the evaporating source and the dispersing torpedo causes the concentrated bundle of electric lines of force to be dispersed. The pattern in which the electric lines of force are dispersed can readily be adjusted by the shape and position of the focusing tube and the dispersing torpedo, the magnitude of electric potential applied, and so on. When the position and shape of the said elements and the magnitude of potential are suitably adjusted, the electric lines of force can be focused at specific parts on the article. The vaporized coating material is then ionized and the ionized particles flow along the bundle of electric lines of force and deposit themselves on the surface of the article. Consequently, possible straying of the coating material can be minimized and, at the same time, the thickness distribution of the film of coating material to be deposited on the article can freely be regulated.

Other objects and other characteristic features of the present invention will become apparent from the description to be given in further detail hereinafter with reference to the accompanying drawing.

BRIEF EXPLANATION OF THE DRAWING FIG. 1 is a schematic sectional view illustrating one preferred embodiment of the device to be employed for practicing the plating method of this invention.

FIG. 2 is a schematic sectional view illustrating another preferred embodiment of the device of this invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a boat 1 containing a metal or an insulating material as the coating material is positioned at the lower portion of the space confined by a bell jar or some other transparent glass cover 3. An article 2 desired to be plated is fixed in position above the said boat 1. The atmosphere enclosed with the cover 3 is composed of an inert gas having a degree of vacuum on the order of 10 to 10 torr. The boat 1 is provided with a heating device (not illustrated) designed to fuse the coating material contained in the boat. When a DC electric potential is applied between the boat 1 as the anode and the article as the cathode, there occurs glow discharge. Consequently, the coating material vaporized in the boat 1 is ionized and the ionized particles of coating material flow along the electric lines of force formed between the two electrodes and deposit themselves on the article 2 which is now serving as the cathode.

In the space intervening between the boat 1 and the article 2, a focusing tube 4 is disposed so as to encircle the circumference of the bundle of electric lines of force formed in the electric field between the two electrodes. When a positive potential is applied to this focusing tube 4, this tube functions as an electrostatic lens to concentrate the electric lines of force emanating from the boat 1 as illustrated. A dispersing torpedo 5 is disposed at the center of the bundle of electric lines of force. When a positive potential is applied to this torpedo 5, the electric lines of force which have been concentrated are dispersed. The pattern in which the electric lines of force are concentrated and then dispersed can easily be regulated by the shape and position of the focusing tube 4 and the dispersing torpedo 5 and the magnitude of potential applied. The vaporized coating material, therefore, is ionized and the ionized particles flow along the electric lines of force formed in the electric field between the two electrodes and deposit themselves on the article 2 which is playing the part of an cathode. Optionally, an exclusive cathode may be incorporated separately of the article so that the courses of the electric lines of force to the article can be varied as desired.

The focusing tube 4 and the dispersing torpedo 5 are not always required to be made of a metallic material. They may be made of other suitable materials Particularly when the focusing tube 4 is formed by using such a transparent material as glass, the tube permits direct observation of the vaporizing source, for example. This is quite advantageous because the transparent wall of the focusing tube 4 does not obstruct the attendants inspection of the interior of the tube. When the focusing tube is formed of such nonconducting material, an annular piece 6 of a conductive material may be attached to a part of the tube. In the first cycle of plating operation, when the coating material is fused and scattered, the scattered coating material is deposited in the form of a translucent film on the outer surface of the nonconducting focusing tube, permitting the tube to acquire conductivity. In the subsequent cycles of plating operation, the electric lines of force can be focused by loading a stated amount of electrostatic potential on the film of coating material thus formed on the tube. Consequently, the flow of the ionized particles of coating material can be directed to a desired destination and the focusing tube can be prevented from further deposition of coating material. The focusing tube, therefore, retains its translucent condition thereafter.

Similarly to the focusing tube 4 of a nonconducting material mentioned above, an annular piece 7 of a conductive material may be attached to one portion of the inside wall of the transparent glass-made cover 3 such as a bell jar in order to prevent the scattered coating material from forming a film on the inside wall and imparing the transparency of the cover as well as to improve the efficiency of plating operation. Either in the first cycle of plating operation or prior to the first plating operation, the scattered coating material may be deposited in the form of a translucent film on the inside wall of the cover. In the subsequent cycles of plating, a required amount of electrostatic potential is applied through the aforementioned piece 7 so that the courses of the electric lines of force may be directed inwardly. Consequently, further deposition of the coating material on the inside wall of the cover 3 can be prevented and, at the same time, possible straying of the coating material can effectively be prevented.

The preferred embodiment described above represents a case in which the electric lines of force are electrostatically focused and dispersed by loading electrostatic potential on the focusing tube and the dispersing torpedo. In case where a focusing coil is utilized as a magnetic-field lens in place of the focusing tube, the electric lines of force can be focused and dispersed in substantially the same way.

In plating a given article with an alloy, if the alloy repared in advance by combining required elements in a desired proportion is placed in the boat 1, fused and deposited on the article, then the element having the lowest vaporizing point is vaporized first. Thus, it becomes difficult to obtain a film of coating material having a uniform composition throughout and it is also difficult to have the composition ratio of elements freely adjusted as desired. If the component elements of the alloy can be vaporized at a fixed proportion, the alloy composition of the film will become uniform throughout all parts of the surface of the article. Accordingly,

it is not possible to obtain a coating having the composition ratio of component metal elements partially varied or to have the composition ratio of component elements of the alloy freely varied along the depth of the formed film of coat.

A solution to this problem may be offered by disposing the same number of boats 1, l as that of component metal elements of the alloy as illustrated in FIG. 2 and placing thereover masks 8, 8' containing holes adjustable in aperture at corresponding positions.

By heating a plurality of boats disposed separately of one another as described above, the vapors of the metals which are used as coating materials are deposited on the surface of the article in amounts proportional to the aperatures of the holes provided in the masks 8, 8'. The amounts of the vapors of metals to be generated may be adjusted by controlling the temperatures at which the individual boats are heated by the heating unit (not shown) instead of using the same mask. ln still another possible modification, the coating metal may be vaporized by heating with irradiation of electron beams, the resultant vapor of the metals converted into a plasma by means of a separate ionization electron gun and the ions of this plasma made to flow in a directed course by means of an ion-extracting electrode so as to allow the ions. to be deposited on the article.

In the aforementioned embodiment wherein the same number of boats as that of the component metal elements composing the alloy are disposed so as to vaporized the coating materials separately of one another, the plating operation may be controlled so that the composition ratio of the component metal elements to be deposited on the article will freely be adjusted or the generation of the vapors of component metal elements will be regulated in timing so as to vary the composition ratio of alloy elements freely along the depth of the film.

A film of alloy having a composition entirely different from that of any ordinary alloy can be obtained when the film of alloy thus deposited on the article is peeled off the article by a suitable method.

Under the cover 3, the plating operation is conducted in the atmosphere of a rare gas having a degree of vacuum on the order of 10 to 10 torr. Conventionally as the rare gas for such plating, there -has generally been employed argon gas. Argon gas has a property of causing the phenomenon of sputtering. In the atmosphere of argon gas, therefore, it is not always possible to perform effective plating because the coating material already deposited on the article may possibly be re moved by the sputtering action of argon ions. this invention capitalizes on this sputtering action of argon gas. To be specific, argon gas is introduced prior to the actual plating operation so as to have the surface of the article cleaned by the sputtering action of argon gas and, after completion of this cleaning, helium gas which shows scanty sputtering characteristics is introduced to replace the argon gas in preparation for the plating operation.

Since the plating is performed in the atmosphere of helium gas on the article which has in advance been cleaned with argon gas, possible removal of the film of coating material already deposited on the article can be minimized and the efficiency of plating heightened accordingly.

As the plating operation is repeated frequently, all the parts of the device that are inside the cover are gradually defiled with the material used as the coating material. The defilement can be a cause for the impairment of plated surfaces or the degradation of vacuum within the cover. To give the article a plated surface of excellent quality, it is extremely important that the whole interior of the device should be cleaned. The said defilement with the coating metal results when some portion of the vaporized coating metal deviates from the directed courses and settles on the parts inside the cover. Thus, the coating metal adheres so strongly that it is extremely difficult to remove the deposited metal mechanically.

According to this invention, the removal of the coating metal which has thus been deposited as a defiling matter on the internal parts is accomplished by allowing glow discharge to be generated in the atmosphere of a rare gas enclosed with the cover of the device, with the deposited coating metal serving as the cathode. In the case of the illustrated embodiment, a switch 9 is provided in the device so that the film of coating metal deposited on the inside wall of the bell jar is energized as a cathode via the annular piece 7 by means of this switch. The film of coating metal which is deposited on the other parts of the device can similarly be energized as cathodes. The vaporizing source and the article which are expected to serve as electrodes at the time of plating are only required to be mutually reversed in polarity.

When the glow discharge is generated by utilizing, as a cathode, the film of coating metal deposited as a defiling matter, the deposited coating metal will completely be removed from the inside wall of the device by virtue of the sputtering of the rare gas ions after a short period of glow discharge. The removed coating metal is then pumped out of the device by a pump (not illustrated). By this treatment, the interior of the device can be thoroughly cleaned. Since argon gas has a high sputtering property, it is suited for the removal of defilement inside the device.

As is apparent from the foregoing explanation, the ionization electrostatic plating method of the present invention lessens the amount of the coating material which is scattered and lost and remarkably improves the efficiency of plating and, at the same time, permits control of the thickness distribution of the coating material formed on the article being plated. Since the amount of the coating material which is scattered around outside the directed courses is small, the vacuum device is defiled very little and time and labor which would otherwise be required for the recovery and removal of stray coating material can be saved. Further, the focusing tube and the cover both made of a transparent material can be prevented from adhesion of coating material and, therefore, can maintain transparency. Thus, the plating can be carried out while a constant watch is kept on the inside of the device. Since the plating method of this invention causes the coating material to be deposited on the article after the surface of that article has in advance been cleaned by the sputtering action of the argon gas, the film of coating material adheres very strongly to the surface of the article.

Possible scattering of the coating material caused by the sputtering action of gas can be prevented and the efficiency of plating improved accordingly, because the plating operation is conducted in the atmosphere of helium gas. In the interval between the time the surface of article is cleaned and the time the coating material is deposited thereon, there is carried out a simple operation of switching gases in the atmosphere enclosed with the cover. Thus, the cleaned surface of the article is not defiled again. No special device is required and the operation is comparatively simple.

What is claimed is:

1. In an ionization electrostatic plating method wherein a DC electric potential is applied in the atmosphere of a rare gas between an anode which is a boat containing a coating material and a cathode which is an article subjected to plating so that glow discharge is generated and then the coating material in the boat is vaporized and the vaporized coating material is deposited on the article, the improvement comprising focusing the electric lines of force occurring in the electric field between said two electrodes by means of a focusing tube, and thereafter dispersing the electric field by means of a dispersing torpedo additionally disposed between the two electrodes, the vaporized gas being ionized and the ionized particles being caused to flow along said electric lines of force and to settle fast on the article.

2. An ionization electrostatic plating method according to claim 1 wherein a positive electric potential is applied to the focusing tube and the dispersing torpedo.

3. An ionization electrostatic plating method according to claim 1 wherein the focusing tube is made of a transparent material and the coating material is deposited thereon in the form of a translucent film so as to confer electro-conductivity upon the focusing tube.

. 4. An ionization electrostatic plating method according to claim 1 wherein the deposited coating is an alloy, the same number of boats as that of component metal elements of the alloy are provided and the component metal element are placed one in each boat so that the individual metal elements are vaporized by being heated separately of one another whereby a film of alloy is consequently deposited on the article.

5. An ionization electrostatic plating method according to claim 1 wherein, during coating, a film of coating material coats the apparatus and a glow discharge is generated by using as the negative electrode the film of coating material deposited on the apparatus thereby removing the deposited coating metal by the sputtering action of the ions of the rare gas in the atmosphere.

6. An ionization electrostatic plating method according to claim 1 wherein cleaning of the surface of the article is effected by the sputtering action of argon gas ions, subsequently replacing argon gas with helium gas to effect plating of the article.

7. An ionization electrostatic plating method according to claim 1 wherein the dispersing torpedo has a triangular shaped cross section configuration. 

1. IN AN IONIZATION ELECTROSTATIC PLATING METHOD WHEREIN A DC ELECTRIC POTENTIAL IS APPLIED IN THE ATMOSPHERE OF A RARE GAS BETWEEN AN ANODE WHICH IS A BOAT CONTAINING A COATING MATERIAL AND A CATHODE WHICH IS AN ARTICLE SUBJECTED TO PLATING SO THAT GLOW DISCHARGE IS GENERATED AND THEN THE COATING MATERIAL IN THE BOAT IS VAPORIZED AND THE VAPORIZED COATING MATERIAL IS DEPOITSED ON THE ARTICLE, THE IMPROVEMENT COMPRISING FOCUSING THE ELECTRIC LINES OF FORCE OCCURRING IN THE ELECTRIC FIELD BETWEEN SAID TWO ELECTRODES BY MEANS OF A FOCUSING TUBE, AND THEREAFTER DISPERSING THE ELECTRIC FIELD BY MEANS OF A DISPERSING TORPEDO ADDITIONALLY DISPOSED BETWEEN THE TWO ELECTRODES, THE VAPORIZED GAS BEING IONIZED AND THE IONIZED PARTICLES BEING CAUSED TO FLOW ALONG SAID ELECTRIC LINES OF FORCE AND TO SETTLE FAST ON THE ARTICLE.
 2. An ionization electrostatic plating method according to claim 1 wherein a positive electric potential is applied to the focusing tube and the dispersing torpedo.
 3. An ionization electrostatic plating method according to claim 1 wherein the focusing tube is made of a transparent material and the coating material is deposited thereon in the form of a translucent film so as to confer electro-conductivity upon the focusing tube.
 4. An ionization electrostatic plating method according to claim 1 wherein the deposited coating is an alloy, the same number of boats as that of component metal elements of the alloy are provided and the component metal element are placed one in each boat so that the individual metal elements are vaporized by being heated separately of one another whereby a film of alloy is consequently deposited on the article.
 5. An ionization electrostatic plating method according to claim 1 wherein, during coating, a film of coating material coats the apparatus and a glow discharge is generated by using as the negative electrode the film of coating material deposited on the apparatus thereby removing the deposited coating metal by the sputtering action of the ions of the rare gas in the atmosphere.
 6. An ionization electrostatic plating method according to claim 1 wherein cleaning of the surface of the article is effected by the sputtering action of argon gas ions, subsequently replacing argon gas with helium gas to effect plating of the article.
 7. An ionization electrostatic plating method according to claim 1 wherein the dispersing torpedo has a triangular shaped cross section configuration. 